1. Field of the Invention
This invention relates generally to controlling the actuation of a transmission control element actuated by the piston of a hydraulic servo on the basis of the piston's position during a gear shift.
2. Description of the Prior Art
Knowing input shaft torque or output shaft torque is considered beneficial for improving the quality of gear shift control of an automatic transmission for a vehicle. Measurement of input shaft torque or output shaft torque allows feedback control that is more robust to unknown disturbances to be utilized. However, the conventional approach of error-based closed-loop (CL) control has limited authority during fast transients in the torque-transfer phase of a gearshift due to the clutch actuators' considerable nonlinearity, delay and lag.
A method for determining clutch torques during a gearshift using references to input and output shaft torque measurements or estimates, providing multiple opportunities for improving shift control exist. While the off-going clutch torque signal and on-coming clutch torque signal provide valuable feedback, essential for changing the whole paradigm of synchronous torque transfer control, that feedback is still not available during the initial phases of clutch actuation.
The clutch has torque carrying capacity only after certain nonlinear dynamic transients in the clutch actuator take place and, unfortunately, there is no feedback information during that transient response. To be able to command the clutch actuator during those initial phases in a robust fashion, knowledge of the internal state of the actuator would be essential.